1. Field of the Invention
The present invention relates to a map display apparatus which displays a map in a bird's-eye view format and converted from a map in a plane view format.
2. Description of the Related Art
There are map display apparatuses for vehicles in the prior art that display a road map on a display device in the so called bird's-eye view display format, whereby a road map in the vicinity of the current position of the vehicle is displayed magnified compared to the portions of the map in the distance (refer to U.S. Pat. No. 5,161,886). The apparatus disclosed in the publication mentioned above sets a viewpoint to the rear of the current position of the vehicle and displays, on the screen of a display device, roads viewed from this viewpoint looking down in the advancing direction of the vehicle. In such a bird's-eye view display, the road map in the vicinity of the current vehicle position can be displayed enlarged and, since a wide range of area from the current position to distant positions can be displayed, it is easy to visually read the connection state and so forth on the road map. Moreover, a road map can be displayed in such a realistic manner that the driver will feel as if he were looking down at the road himself.
In order to display a road map in the bird's-eye view format, road maps for bird's-eye view display may be stored in a CD ROM or the like in advance. However, since the map scale constantly changes with a bird's-eye view as the viewpoint moves, the quantity of data required for the road map becomes massive. Because of this, it is a general practice to convert road map data for normal planar map display to bird's-eye-view data for display. However, since the conversion calculation to obtain bird's-eye-view data must be performed every time the position of the viewpoint moves, screen redraw becomes slow and this could detract from ease of use.